Voice over for series of training videos based on MS Powerpoint

I need a subtle professional (not posh) deep/ mature UK male voice over for a short series of training video units based on a MS Powerpoint presentation. The videos are part of an e-learning course for 'tyre technicians' that is already up & running, with 'amateur' narration, but this needs replacing. The audience is predominantly male & of a 'manual' (not academic) background so narration needs to be clear & measured. The make-up of the Powerpoint videos are shown below. Running time is 99 slides & currently approx. 90 mins in total. I have a script for the entire course.
Unit 0 Welcome 11 slides
Unit 1 Introduction 9 slides
Unit 2 About tyres 11 slides
Unit 3 Tyre structure 8 slides
Unit 4 UK tyre law & the MOT 22 slides
Unit 5 Tyre repairs 12 slides
Unit 6 PWTs 26 slides
I am assuming (perhaps incorrectly) that the output from you would be a separate text file for each slide that I can simply attach & then converted to video. I have no experience of video or audio editing & do not have the time to start now. So I am looking for an easy solution. I can provide copies of the current 7 videos or Powerpoint files which can be edited with the new voice-over, or am open to alternative suggestions.
If this proves successful I have 2 other similar (but longer) courses already running (but which also needs new narration) plus a further course in development.
Obvs. I will want to hear sample voice overs before selecting.